Split packages in ModbusMasterTcpConnection #174

private async Task HandleRequestAsync()
{
	while (true)
	{
		Debug.WriteLine($"Begin reading header from Master at IP: {EndPoint}");
		
		int readBytesTotal = 0;

		while (readBytesTotal < 6)
		{
			int readBytes = await Stream.ReadAsync(_mbapHeader, readBytesTotal, 6 - readBytesTotal).ConfigureAwait(false);
			
			if (readBytes == 0)
			{
				Debug.WriteLine($"0 bytes read, Master at {EndPoint} has closed Socket connection.");
				ModbusMasterTcpConnectionClosed?.Invoke(this, new TcpConnectionEventArgs(EndPoint));
				return;
			}

			readBytesTotal += readBytes;
		}

		ushort frameLength = (ushort)IPAddress.HostToNetworkOrder(BitConverter.ToInt16(_mbapHeader, 4));
		Debug.WriteLine($"Master at {EndPoint} sent header: \"{string.Join(", ", _mbapHeader)}\" with {frameLength} bytes in PDU");
		
		_messageFrame = new byte[frameLength];

		readBytesTotal = 0;

		while (readBytesTotal < frameLength)
		{
			int readBytes = await Stream.ReadAsync(_messageFrame, readBytesTotal, frameLength - readBytesTotal).ConfigureAwait(false);
			
			if (readBytes == 0)
			{
				Debug.WriteLine($"0 bytes read, Master at {EndPoint} has closed Socket connection.");
				ModbusMasterTcpConnectionClosed?.Invoke(this, new TcpConnectionEventArgs(EndPoint));
				return;
			}

			readBytesTotal += readBytes;
		}

		Debug.WriteLine($"Read frame from Master at {EndPoint} completed {readBytesTotal} bytes");
		byte[] frame = _mbapHeader.Concat(_messageFrame).ToArray();
		Debug.WriteLine($"RX from Master at {EndPoint}: {string.Join(", ", frame)}");
		
		var request = ModbusMessageFactory.CreateModbusRequest(_messageFrame);
		request.TransactionId = (ushort)IPAddress.NetworkToHostOrder(BitConverter.ToInt16(frame, 0));

		// perform action and build response
		IModbusMessage response = _slave.ApplyRequest(request);
		response.TransactionId = request.TransactionId;

		// write response
		byte[] responseFrame = Transport.BuildMessageFrame(response);
		Debug.WriteLine($"TX to Master at {EndPoint}: {string.Join(", ", responseFrame)}");
		await Stream.WriteAsync(responseFrame, 0, responseFrame.Length).ConfigureAwait(false);
	}
}